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Omron Relays at Digikey

Oilmaster said:
That's a good reference photo to work from. Quite strange marking it is, because the LY relays are for DC only made as 12/24/48/100/110V, in which the marking is normally something like LY2-0-DC24 (the 0 in the middle stands for PCB pin).

That marking of yours may suggest a custom version made for Technics, perhaps 20Vdc (but why?)

Now, the LY datasheet states that the "must-operate voltage" is at 80% max, meaning that a 24Vdc relay will always be on at 19.2V; so a regular 24 Vdc relay may work if your original relay would be 20Vdc. A bit of circuit tweaking might help things further (or alternatively to lower the voltage to the relay to 12V so that a 12V relay could be installed)

But before anything else, some circuit diagram would be required.
Or simpler.... measuring the voltage across the existing relay while it is on... that would solve the voltage rating question very quickly.
Click to expand...

I will just turn it on and measure it. I will do one more off check on the power supply, and then will turn it on without power amp assembly installed (then I will reinstall the rebuilt power amp section).
I do not see enough information on the schematic to determine voltage across the coil (I can see 70.7 VDC coming off the bridge to one side of the coil, but the other is connected to collector of a transistor in protection board - so that transistor opening/closing would determine the current through the coil and hence the voltage across it).

It does sound like it's a 20 VDC coil, and 24 VDC coil relay should work, but we will know for sure. And no markings on the coil tape - just like the one in the auction. It's a common relay in a lot of Technics receivers, so I'm surprised this question didn't come up before. There is a guy from Europe who is selling replacement relay on ebay, but of course his photos do not display the new relay p/n.
 
I downloaded the service manual to see what's going there.
Indeed the relay is fed from the +70.7V power rail, switched on/off by TR111 (having around 0.7V voltage drop around it), with a 2W 1.2K resistor in series.

So, simply put, the resistor and relay together drop 70V, with the question how much by the relay, which depends very much on the actual resistance of the relay's coil.

It would be good if you measure:
- the voltage drop across the relay
- the actual tension in between R726 and the relay (or voltage across R726)
- once the relay is taken out: the resistance of the coil

Even if this relay is an oddball version, it is easy to adapt the circuit to a regular 24Vdc or 48 Vdc relay by adapting R726, but for that above three measurements are required.

Note: the relay will most likely not engage when the amp boards are removed; those relays are only engaged when the entire amp is healthy with limited DC offset present. So you have to do the first two measurements with the unit fully functional.
 
Oilmaster, if I measure the DC resistance of the coil, would it make sense to take that resistance, with in-series R726 of 1.2KOhm; then take total voltage drop across the whole circuit of 70V. Then just use Ohm's law to calculate voltage drop across the coil?

I took LY2-0-DC24 as an example. DC resistance of the coil is 650 Ohm. With 70V across the circuit, and with 1.2KOhm resistor in series, I get 24.6V drop across the resistor coil.

Just for secondary check, resistor is 2-watt max rated; so with 70V applied to the circuit, I get 1.7 watt dissipation on this resistor. It kind of makes sense, but makes the resistor very toasty.

I will measure the DC resistance of the coil in my receiver when I'll get home tonight to confirm.
 
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Exactly my thinking this afternoon :)
Just work your way back starting with a new standard relay all together

Without adapting the resistor, the relay would see a bit high voltage (no panic though, but getting warmer) as well as the resistor gets a bit too well used.

Increasing its value to 1300 ohm , the relay voltage will be 23.2V (perfect), and 1.65W dissipation
Just buy a metal oxide 3~5W resistor with the new relay (and give it air to cool)

Increasing the resistor to 1400 ohm should work as well, relay voltage to 22.2V and 1.62W resistor dissipation.
I think the latter would be my choice to have less relay coil warm up.
 
So the original relay coil resistance is 625 Ohm. Pretty much spot on, the voltage drop is at 23.9V then, assuming supply voltage is 70V.

Looks like LY2-0-DC24 is the proper replacement relay, even with original 2W resistor. Or as you said, bump the reistance to 1.4k / 5W.

Thank you for your help! Ordered relay this morning (obviously didn't order resistors, but will get them from a local shop). Funny note: relays are exactly 1/2 price at mouser compared to digikey (except shipping to Canada is 20 instead of 8).
 
Hm, looks like I will need another LY2-0-DC24 relay lol. Or could be MY4-02-DC24 or MY2- can't see the pinout yet.

Marantz 1070 relay is shot - getting 24VDC to the coil, coil resistance is 640 Ohms. Relay doesn't pick - at least I don't hear a click, and to verify contacts making will have to disassemble the entire amplifier board assembly.
 
ViperZ said:
Marantz 1070 relay is shot - getting 24VDC to the coil, coil resistance is 640 Ohms. Relay doesn't pick - at least I don't hear a click, and to verify contacts making will have to disassemble the entire amplifier board assembly.
Click to expand...
Thats doesn't mean the relay is bad. 24 vdc is always present on one end of the relay coil and measured at both ends of the coil until relay "sets". H727 and H 728 controls the other end of the coil.By routing the 24 volts through the coil to ground to "set" the relay. Or removing the ground to "reset" the relay. The protect circuit may be operating as it should. Have you checked your DC offset voltages from the amplifiers ? At a point before the relay of course.
With the relay "set" 24vdc will be measured on one end of the relay and near zero volts on the other.
 
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avionic said:
Thats doesn't mean the relay is bad. 24 vdc is always present on one end of the relay coil. H727 and H 728 controls the other end of the coil.By routing the 24 volts through the coil to ground to "set" the relay. Or removing the ground to "reset" the relay. The protect circuit may be operating as it should. Have you checked your DC offset voltages from the amplifiers ? At a point before the relay of course.
Click to expand...

Thank you for pointing out that 24vdc is always there, just double checked it.

I see around 1mv on r775 and r776, which are outputs just before the relay.

I also see 0.7v on collector of h728, 1.3v on base of h727. Those are all spot on.

I might just inject the signal into input and see of it gets to r775 and 776 first...
 
727 emitter is 0.7v .

I injected the signal through main in and can see it on resistor 775 and 776 (edited - both channels get to the relay)
Also weird is that DC offset seems to be right at 0 on both channels, almost too good to be true. Idle current in both channels is at 20mV. I can adjust it, but it should not trigger protection at this value .
 
I did some research on the relay - there are quite a few threads on AK about it failing, but nobody found a form-fit-function replacement.

LC2-C-M relay - 640 Ohm 24VDC coil. I have never seen such a pin configuration in protection relay - 2 top pins for the input, middle pins for coil, bottom pair for outputs... None of the LY2 or MY4 series that I can find have this pinout. I really don't think the "paper cleaning trick" is a long term solution. I may macgyver LY2 instead - epoxy the relay nearby and hardwire it into the board? Would that make sense?
 
ViperZ said:
I did some research on the relay - there are quite a few threads on AK about it failing, but nobody found a form-fit-function replacement.

LC2-C-M relay - 640 Ohm 24VDC coil. I have never seen such a pin configuration in protection relay - 2 top pins for the input, middle pins for coil, bottom pair for outputs... None of the LY2 or MY4 series that I can find have this pinout. I really don't think the "paper cleaning trick" is a long term solution. I may macgyver LY2 instead - epoxy the relay nearby and hardwire it into the board? Would that make sense?
Click to expand...
Before jumping the gun.. Replace H728...I think your relay is good. Granted it may have tarnished or pitted contacts. But replacing it won't make it " click" nor will cleaning/burnishing the contacts.

ViperZ said:
Relay doesn't pick - at least I don't hear a click,
Click to expand...
 
I will continue troubleshooting tomorrow. Will get the relay out. I'm pretty sure about coil DC resistance value. That 640 ohm value is dominating resistance in that circuit.
Regarding voltage at 728 base, I'll try to get there, it's hard to measure, but why would it be different from value I measured on the other transistor?
 
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